High strength flooring compositions

ABSTRACT

A composition is disclosed for a mixture to be used in conjunction with water for preparing a slurry that hydrates to form a high strength flooring compound. The mixture includes from about 50% to about 98% by weight calcium sulfate hemihydrate, having at least 25% of the calcium sulfate hemihydrate in the beta-calcined form. A polycarboxylate dispersant is included in the mixture in amounts from about 0.2% to about 10% by weight. The mixture also includes 0.05–50% by weight enhancing component. When combined with recommended amounts of water, a slurry is formed that is useful as a flooring composition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application60/367,920, filed Mar. 27, 2002.

BACKGROUND

This invention relates to a high strength flooring composition. Morespecifically, it relates to a flooring composition made usingbeta-calcined calcium sulfate hemihydrate.

Both gypsum and cement are well known as construction materials. Gypsumis the principal component of the familiar wallboard, where is it facedwith paper to provide strength and a smooth surface. Cement is used invarious applications where its water resistance and hardness areimportant, such as in concrete structures. Cement is also used inbuilding panels where its hardness and water resistance are important.

Gypsum is also known as calcium sulfate dihydrate, terra alba orlandplaster. Plaster of Paris is also known as calcined gypsum, stucco,calcium sulfate semihydrate, calcium sulfate half-hydrate or calciumsulfate hemihydrate. Synthetic gypsum, which is a byproduct of flue gasdesulfurization processes from power plants, may also be used. When itis mined, raw gypsum is found in the dihydrate form. In this form, thereare approximately two water molecules of water associated with eachmolecule of calcium sulfate. In order to produce the hemihydrate form,the gypsum can be calcined to drive off some of the water of hydrationby the following equation:CaSO₄.2H₂O→CaSO₄.1/2H₂O+3/2H₂O

When mixed with water, the hemihydrate rehydrates to form aninterlocking matrix of interlocking dihydrate crystals. Gypsum hydrationoccurs in a matter of minutes or hours compared to several days forcement. This makes gypsum an attractive alternative for cement forflooring applications if sufficient hardness and strength can beachieved in the gypsum.

Calcium sulfate hemihydrate can produce at least two crystal forms.Alpha-calcined gypsum is made by a continuous process or lump rockprocess whereby the calcium sulfate dihydrate is calcined underpressure. The alpha-calcined gypsum forms less acicular crystals thanbeta-calcined gypsum, allowing the crystals to pack tightly together,making a denser and stronger plaster. The crystal morphology allowswater to flow easily between the crystals, requiring less water to forma flowable slurry. More elongated crystals are characteristic of thebeta-calcined gypsum. This crystal structure results in a less denseproduct because the crystals are more loosely packed. The beta form alsorequires more water to fluidize the calcined gypsum. In applicationswhere hardness is important, alpha-calcined gypsum is usually preferred,despite higher cost and limited availability.

When choosing a calcined gypsum for an application, beta-calcined gypsumis often selected due to its ready availability and its reduced cost.Because beta-calcined gypsum is also more common, it can incur reducedshipping and storage costs than the alpha form. However, the crystalstructure makes it difficult to make a strong, dense gypsum because morewater is needed to produce a slurry of a given fluidity.

Superplasticizer additives are known to improve the fluidity of a gypsumslurry. They disperse the molecules in solution so that they move moreeasily relative to each other, thereby improving the flowability of theentire slurry. Sulfonated melamines and sulfonated naphthalenes areknown as superplasticizers, however, the improved fluidity obtained isnot sufficient to permit complete substitution of beta-calcinedhemihydrate for alpha-calcined hemihydrate in high strength flooringapplications.

BRIEF DESCRIPTION OF THE INVENTION

Polycarboxylates are also known as superplasticizers for use withcement. However, when used together with an enhancing component,polycarboxylates perform far better than conventional superplasticizers,such as sulfonated naphthalenes or sulfonated melamines.

More specifically, an embodiment of this invention is a mixture to beused in conjunction with water for preparing a slurry that hydrates toform a high strength flooring compound. The mixture includes from about50% to about 98% by weight calcium sulfate hemihydrate, having at least25% of the calcium sulfate hemihydrate in the beta-calcined form. Apolycarboxylate dispersant is included in the mixture in amounts fromabout 0.2% to about 10% by weight. The mixture also includes 0.05–50% byweight enhancing component. When combined with recommended amounts ofwater, a slurry is formed that is useful as a flooring composition.

In another embodiment of this invention, fast drying flooringcompositions are obtained by reducing the water to less than 25% of theweight of the dry ingredients. Use of alpha-hemihydrate for up to 100%the total hemihydrate is preferred.

The present composition results in formation of a high-strength flooringeven when 100% beta-calcined hemihydrate is used. In the presence of theenhancing component, the polycarboxylate dispersant is more effectivethan other superplasticizers, making the slurry more fluid and flowable.Fluidity of the mixture is so good that beta-calcined gypsum isfluidized in the slurry at low water usage to make a denser, strongerflooring product than is known in the art.

DETAILED DESCRIPTION OF THE INVENTION

A mixture for making a slurry suitable for use in flooring applicationsis made from calcium sulfate hemihydrate, an enhancing component and apolycarboxylate dispersant. High strength floors and subfloors are madewith this composition having compressive strength in excess of 2500pounds per square inch (175 Kg/cm²). In a preferred embodiment describedin detail below, all components of the composition are described interms of dry ingredients in a dry mixture. It is contemplated that thisis only one possible embodiment, and that liquid ingredients, whenmeasured on a dry solids basis, are equivalent to the dry components.Unless otherwise stated, all components are measured in terms of weighton a dry solids basis, excluding any aggregate or fillers that may bepresent.

The primary component of the dry mixture is calcium sulfate hemihydrate.The dry mixture composition preferably includes from about 50% to about98% hemihydrate by weight. More preferably, from about 80% to about 98%,from about 80% to about 95% or from 88% to about 95% of the dry mixtureis calcium sulfate hemihydrate.

Any type of hemihydrate is useful in this mixture. It can be prepared byany known process, such as slurry processes, lump rock processes oratmospheric calcination methods. Either alpha calcined calcium sulfatehemihydrate or beta calcium sulfate hemihydrate are useful in themixture. The alpha form of calcium sulfate hemihydrate crystals is lessacicular in shape than the beta version. The less acicular shape allowsthe crystals to wet out and flow much better when mixed with water. Thelower water demand of the alpha form results in a more closely packed,and higher density composite in comparison to the resultant interlockingmatrix of calcium sulfate hemihydrate crystals utilizing the beta formof calcium sulfate hemihydrate. As is known in the art, the combinationof alpha and/or beta calcium sulfate hemihydrate controls the amount ofwater needed to form a workable slurry, which controls the density ofthe final cast model.

Any alpha or beta-calcined hemihydrate is suitable for use in thepresent composition. Preferred alpha-hemihydrates include those madefrom a slurry process, such as HYDROCAL C-Base, J-Base or E-Base fromUnited States Gypsum Company (Chicago, Ill.), by lump rock processes,such as HYDROCAL A-Base or B-Base, or any other method of makingalpha-calcined hemihydrate. No. 1 Moulding plaster is a preferredbeta-hemihydrate from United States Gypsum Co. (Chicago, Ill.).Continuously calcined synthetic gypsum is equivalent to beta-calcinedhemihydrate. Beta-hemihydrate made from other methods is also useful.The addition of soluble calcium sulfate anhydrite is a suitablesubstitute for up to 50% of the hemihydrate, and will serve to makeprovide strength to the matrix. Calcium sulfate dihydrate serves as afiller and should be used only in minor amounts, less than 25% by weightof the hemihydrate.

Whether beta-calcined gypsum, alpha-calcined gypsum or a combination ofalpha and beta is selected for a particular application depends on anumber of factors. Preferably, beta-calcined gypsum is used to a largeextent where cost is a primary concern. Beta-calcined gypsum also hashigher workability and bleeds less than the alpha form. However, in someembodiments, where even higher strength is desirable, thealpha-hemihydrate or mixtures of the alpha and beta forms are preferred.Where mixtures of alpha and beta-calcined hemihydrate are used, themixture should include at least 25% beta-hemihydrate. Preferably, theamount of the beta-calcined form is greater than 50% or greater than 90%of the total hemihydrate.

The enhancing component is at least one of cement and lime. When testedwith gypsum in the absence of cement or lime, polycarboxylates haddispersing properties comparable to those of other well-knowndispersants. However, when combined with an enhancing component, thepolycarboxylate surprisingly displays even greater dispersionproperties.

At least one enhancing component must be present to obtain theextraordinary performance from the polycarboxylate. Preferred enhancingcomponents include lime and hydraulic cement. At least 0.05% lime or anequivalent alkaline material is required. Generally, the enhancingcomponent is present in amounts of from about 0.05% to about 10% if itis not a hydraulic material. Preferably, the concentration of lime isless than 2.5% or less than 1% by weight of the dry ingredients. The useof two or more enhancing components is also contemplated. In a drypowder form, lime is convenient for the addition to the preferred drymixture, however, it is also contemplated that liquid forms are alsouseful, and could be added to the water prior to addition of the drymixture. If a liquid is used, the amount of alkaline material should bemeasured on a dry solids basis and any water should be considered in thewater content of the slurry.

If the enhancing component is cement or other siliceous hydraulicmaterial, amounts up to 50% of the dry mixture can be used. Like gypsum,hydraulic cement hardens be a chemical interaction with water. Exemplaryhydraulic cements are Portland cement, fly ash, blast furnace slag, andsilica fume. The most widely used cement is Portland cement (AalsborgCement, Denmark), which is particularly preferred for use in thisinvention. More preferred cements are Type 1, Type 3 and Type 5 cements.Either gray or white cement can be used. Class C cement, slag cement and#1 Impmill cement are also contemplated for use in this composition.Other hydraulic silicates are also considered to be useful as theenhancing component. If no other enhancing components are present, themixture includes at least 0.5% cement. Preferably the concentration ofcement is from about 1.7% to about 50% by weight of the dry ingredientweight.

The polycarboxylate dispersant is required in concentrations of fromabout 0.2% to about 10% by weight on a dry component basis. Morepreferably, the dry mixture includes from about 0.2% to about 5% orabout 0.2% to about 2.5% of the polycarboxylate.

Polycarboxylates are known for use with hydraulic cement. A wide varietyof polycarboxylates can be used in the dry mixture, including, but notlimited to polycarboxylic acids and acrylic latex polymers. Preferablythe polycarboxylates are water soluble. The polycarboxylate polymerincludes at least two carboxylate salt or ionic groups, at least twocarboxylic acid groups or at least one carboxylate salt or ion group andat least one carboxylic acid group. Molecular weights of from about100,000 to about 5,000,000 Daltons are preferred. Polycarboxylatesoutside the preferred molecular weight range tend to be less effective,while higher molecular weight materials are extremely viscous anddifficult to pump. Methods of making polycarboxylate dispersants arewell known to those skilled in the art.

The polycarboxylate polymers are added in amounts of from about 0.2% toabout 10% by weight. Other preferred ranges include from about 0.2% toabout 5% and from 0.2% to about 2%. The exact amount of polycarboxylatedispersant depends on the composition with which it is used.Polycarboxylates may be used alone or in combination with otherplasticizers including, but not limited to, lignins, sulfonatednaphthalene and/or sulfonated melamine dispersants.

Preferred Polycarboxylates are polymers prepared by polymerization of amonomer mixture that includes an unsaturated carboxylic acid typepolymer. MELFLUX 1641 by SKW Polymers (Kennesaw, Ga.) is a particularlypreferred polycarboxylate. It is a free flowing powder produced byspray-drying a modified polyether carboxylate. Other preferredpolycarboxylate dispersants include MELFLUX 1643 or 1643F (SKW Polymers,Kennesaw, Ga.), which are based on oxyalkylene-alkyl ethers andunsaturated dicarboxylic acid derivatives and are described in U.S. Pat.No. 5,798,425. Other suitable polycarboxylate dispersants includeacrylic resin latexes, modified acrylic polymers such as those describedin European Patent 1,138,698, copolymers of acrylic acid and acrylamide,polymers obtained by grafting substituents such as polyalkylene oxide ona polycarboxylate backbone, poly (methyl vinyl ether/maleic acid) or anypolycarboxylate dispersant known to an artisan.

The amount of water added to the dry mixture ranges from 10% of theweight of the dry mixture to about 50% by weight. Preferably, the watercontent ranges from about 20% to about 40%, from about 12% to about 40%and more preferably from about 28% to about 32%. The selection of asuitable amount of water to be added is within the skill of an artisan.Water usage less than that theoretically needed to hydrate the hydrauliccomponents is used in some embodiments of the composition.

Water used to make the slurry should be as pure as practical for bestcontrol of the properties of both the slurry and the set plaster. Saltsand organic compounds are well known to modify the set time of theslurry, varying widely from accelerators to set inhibitors. Someimpurities lead to irregularities in the structure as the interlockingmatrix of dihydrate crystals forms, reducing the strength of the setproduct. Product strength and consistency is thus enhanced by the use ofwater that is as contaminant-free as practical.

Embodiments to fast drying flooring compositions are also obtainableusing up to 100% alpha-hemihydrate. By reducing the water content, thereis less water to be removed by drying. The preferable water contentranges from about 15% to about 25%. Improvement in the flowability ofthe slurry allows formation of a pumpable slurry at lower water levels,even below that theoretically required for complete hydration of thehemihydrate. In any plaster composition, increased water additiondecreases the strength of the set plaster.

Many additional ingredients are suitable to optimize the dry mixture.Defoamers are used to reduce air bubbles formed during mixing of the drymixture with the water. When used, the dry mixture includes up to 0.5%defoamer. FOAMASTER CN (Astro Chemicals, Kankakee, Ill.) is a preferreddefoamer.

Boric acid is optionally added to the dry mixture to reduce calcinationand mold/mildew growth. Preferably, it is added in amounts up to 1.25%.Other preferable ranges of boric acid addition are up to 1% and up to0.5%.

Retarders are added to increase the working time of the slurry. Targetworking time is from about 10 minutes to about 2 hours depending on thecomposition being used, where and how the slurry is being applied. Anyretarders known to be useful with calcium sulfate hemihydrate aresuitable in amounts to produce working times consistent with the targetrange. Proteinaceous retarders, such as SUMA, Cream of Tartar (potassiumbitartrate), sodium citrate and diethylenetriamine pentaacetic acid arepreferred.

Set accelerators are used to hasten setting of the slurry. Anyaccelerators known to hasten setting of the hemihydrate may be used,including, but not limited to sulfates, acids and calcium sulfatedihydrate. Useful amounts vary with the efficacy of the acceleratorselected, but are generally less than 1% by weight.

Calcium sulfate dihydrate that has been finely ground is a preferredaccelerator. When freshly prepared, it has high potency and is suitablefor immediate use in the slurry. However, when stored prior to use, itloses its effectiveness. U.S. Pat. No. 2,078,198, herein incorporated byreference, discloses improved accelerators comprising calcium sulfatedihydrate intermixed with a material such as sugar. This mixture rendersthe calcium sulfate dihydrate less subject to deterioration by aging andis useful in the slurry within several days (weeks). Heating theco-ground sugar and calcium sulfate dihydrate mixture so thatcaramelized sugar forms a coating on the calcium sulfate dihydrate isdisclosed in U.S. Pat. No. 3,573,947, herein incorporated by reference.The melted sugar coating further stabilizes the calcium sulfatedihydrate, reducing the effects of aging to a greater degree than theunheated sugar/dihydrate mixture. Ground calcium sulfate dihydrateprepared in this manner is referenced in the examples as “CSA” (UnitedStates Gypsum Co., Chicago, Ill.). In any form, the ground dehydrate ispreferably used in concentrations less than 0.5% by weight.

The addition of 0.0006% to about 0.5% polysaccharide improves the sandloading, reduces bleed and settling, and improves pumpability of thecomposition of this embodiment. The use of polycarboylate andpolysaccharides together results in a product that is easy to handle, isuniform and has high strength, a combination of properties that cannotbe achieved by the use of either polymer alone. Polysaccharides also actwith the polycarboxylate dispersants to keep the components of theslurry in suspension until the crystal matrix forms sufficiently toassure uniform distribution. Sand or other aggregates are prevented fromsettling. The slurry is less viscous and easier to pump, therebyreducing energy costs. Workability of the composition and surfacelubricity are also increased.

The polysaccharides that are particularly preferred for use with thisinvention are varied. Biopolymeric gums are most preferred. Glucanproducts, such as scleroglucan, schizophyllan and the like areespecially preferred. Scleroglucan is produced by filamentous fungi ofthe genera Sclerotium. Schizophyllan is an extracellular polysaccharideproduced by fungi of the genera Schnizophyllum. Scleroglucan andschizophyllan are polysaccharides whose linear chain of 1–3 linkedD-glycosyl units with about 30 to about 35 percent of the linear chaincontaining single D-glycosyl units that are attached by 1–6 linkages.The average molecular weight is greater than or equal to 5×10⁶. They arenonionic homopolysacchrides. The chains are self-associated in a triplehelix arrangement. They dissolve in water to form pseudo plasticsolutions. Additional characterization of these compounds and a methodfor making them is taught in U.S. Pat. No. 4,954,440, hereinincorporated by reference. A preferred scleroglucan is marketed by SKWPolymers (Kennesaw, Ga.) under the trade name BIOVIS. Otherpolysaccharide gums, such as xanthan gums, welan gums and other gums arecan also be used with this invention.

Heteropolysaccharides are high molecular weight, generally linearcarbohydrate polymers containing two or more different kinds ofmonosaccharides. The two or more kinds of monosaccharides that form arepeating unit that is polymerized, such as S-657, discussed in U.S.Pat. Nos. 5,175,278 and 6,110,271 herein incorporated by reference. Thispolysaccharide is an example of a xanthan gum that is particularlyuseful in this invention. S-657 forms an extended intertwined 3-foldleft-handed double helix with a molecular weight estimated in excess oftwo million Daltons and is marketed under the trade name Diutan by KelcoBiopolymers (San Diego, Calif.).

When aggregates are added to the composition, any aggregate known tothose skilled in the art may be used. Silica sand and other silicatesare the most common aggregates used due to their low cost and readyavailability. The aggregate can be selected to modify the density of thefinished product. A wide range of sands are applicable with thisinvention, including river sand, Mohawk Medium sand, Rich Mix Fine sand,Atlanta sand, Dothan Sand, Florida sand and the like. Sands of varioustypes can be combined to obtain specific particle size distribution orother properties. Heavier aggregates, such as, but not limited to, rock,gravel, pea gravel and silica fume increase the density of the product,while the addition of hadite, clay, pumice, foam, vermiculite or hollowmicrospheres decrease the density. Any type of filler, such as perlite,flyash or slag, can also be used. The aggregate is added to thecomposition in amounts up to 300 wt % of the aggregate-free componentson a dry basis.

The compositions of this invention optionally have a number of furtheradditives depending on the specific application. These additives caninclude thickeners, coloring agents, preservatives and other additivesin amounts known in the art. Additives for a particular purpose, as wellas the appropriate concentrations, are known to those skilled in theart. Coloring agents, such as pigments, dyes or stains are also usefulas additives, particularly in flooring applications. Any known coloringagents can be used with this invention. Titanium dioxide is particularlyuseful to whiten the composition. The coloring agents are used inamounts and added by methods conventionally used for compositions ofthis type.

In another embodiment of this invention, the mixture is adjusted to makea self-leveling flooring that requires little or no finishing to producea high quality, level surface. Slurries for use in this application aremore free-flowing. Although the viscosity of the slurry can be reducedmerely by adding water, strength of the finished product is reduced andseparation of the water, known as bleeding is increased. Levelingcompositions generally incorporate a polymeric resin into the slurry andmay require modification of the composition.

Leveling compositions also utilize a polymeric resin to modify thesurface properties of the finished floor. Surface brittleness is reducedwhen polymers are used in concentrations of up to 5%, or preferably fromabout 0.05% to about 1%. Exemplary resins include 10184 and 50E 200 fromElotex AG (Sempach, Switzerland) and VINNAPAS RP-226 (Wacker PolymerSystems, LP, Adrian, Mich.).

It is often advantageous to vary the composition within the scope ofthis invention depending upon the mixing or pumping equipment that isused. Different brands of pumping equipment produce shear forces thatrequire certain properties of the slurry to flow properly. Some machinesutilize aggregate of a specific particle size distribution. Othermachine manufacturers recommend slight changes to the composition.Modifications of the composition to accommodate the equipment isconsidered to be within the skill of one who normally prepares slurriesfor such equipment.

When used as a topical underlayment, the composition is modified to befree flowing and easily pumped through a hose. Higher fluidity isdesired without separation of the aggregate. In this application, waterand the polymeric resin are used at the high end of their concentrationrange. The aggregate should be selected to reduce separation or settlingof the solids in the hose.

Use of these compositions requires no special mixing steps or processconditions to make a high quality product. Ingredients to make the drymixture or the slurry are obtained. Depending on the exact additiveselected, it can be available in either liquid form, dry form or both.If used in liquid form, the additive concentration is determined on adry basis. The present mixture is made by obtaining ingredientscomprising from about 50% to about 98% calcium sulfate hemihydratecomprising at least 25% of the beta-calcined form, from about 0.2% toabout 10% polycarboxylate dispersant and from about 0.05% to about 50%of an enhancing component, all on a dry solids basis. Optional additivessuch as set accelerators, retarders, polymeric resins, defoamers, andthe like, are also assembled. The ingredients are separated into wetingredients and dry ingredients for ease of mixing. The dry ingredientsare blended in a mixer, such as a Marion mixer, until a homogeneousmixture is attained. The dry mixture is optionally packaged for latersale or distribution.

At the site where the floor or subfloor is to be laid, about 12 cc toabout 40 cc of water is measured per 100 grams of the ingredients on adry solids basis, and placed into a mixing vessel. If any wet or liquidingredients are used, they are mixed into the water. The dry ingredientsare then mixed into the water, forming a homogeneous slurry. The slurryis then applied, pumped, dumped or poured onto a substrate and allowedto set, forming the floor or subfloor.

Although this floor product does not require finishing, finishing thesurface is desirable under circumstances as will be known to thoseskilled in the art. Choice of a finishing technique allows the finisherto control the surface properties to some degree, including the surfacewear. The floor is optionally finished by any technique known to cementfinishers, including but not limited to floating, pinrolling orscreeding.

These and other embodiments are demonstrated in the following Examples.In the examples, unless otherwise noted, all amounts listed are inpounds. Concentrations or percentages are calculated on a dry,aggregate-free weight basis.

Several of the examples use a slump test to study the how well anaggregate such as sand is suspended in the slurry. The test is intendedto simulate conditions where a floor is being poured and the slurry ispumped through hoses. Occasionally the pump has to be stopped to switchto a different batch or to move to a different section of the floor.During these times the slurry sits undisturbed in the hose for severalminutes before pumping is resumed. The slump test is intended tosimulate these conditions.

Unless otherwise noted, a 4000 gram sample was prepared based on the drycomponents. All dry components, including aggregate, were weighed anddry blended together. The predetermined amount of deionized water wasmeasured and poured into a mixing bowl. The dry blended material wasadded to the water and the time noted as the starting point to determinethe set time. The mixing bowl was placed onto a Hobart mixer and joggedfor approximately five seconds. After one minute of soaking, thematerial was mixed at low speed for two minutes. The bowl was removedfrom the mixer and the contents stirred for about 15 seconds with a wiskto assure that all material was evenly mixed.

The initial slump sample was poured into a damp 2″×4″ (5 cm×10 cm)cylinder placed on a plastic sheet, slightly overfilling the cylinder.Excess material was screeded from the top, then the cylinder was liftedup smoothly, allowing the slurry to flow out the bottom, making thepatty. The patty was measured (±⅛″) in two directions 90° apart, and theaverage reported as the patty diameter. The remaining sample materialwas permitted to set undisturbed in the pitcher for 5 minutes. Withoutstirring, additional slump samples were poured at five minute intervalsuntil all the material was gone or until the material set and could notbe poured. The mix was not stirred between slump samples.

Bleed water was determined as the excess amount of water on the surfaceof the samples after the material had set. A 130 mL sample was pouredinto a 240 mL set cup and allowed to set until Vicat set was achieved.The cup containing the sample and the bleed water was weighed (±0.10g.). Next, the bleed water was poured off and the cup shaken to removeall excess water. The cup and sample were re-weighed. The bleed waterwas calculated as follows:(Initial Weight−Final Weight)÷Initial Weight*100=% Bleed Water

Aggregated two-inch cubes were used to test density and compressivestrength. Cube molds were prepared by sealing the bottom of the moldwith petroleum jelly to prevent leaking and lubricating the molds withan approved release agent, such as WD-40. Sample material was pouredinto the corner of the cubes until they were approximately ¾ full,stirring to keep the sand suspended if needed. Using a small spatula,the sample material was vigorously agitated from corner to corner for3–5 seconds, eliminating all bubbles in the cube. The cubes were thenfilled to slightly overfull, and the remaining sample material pouredinto the set cup for additional testing. Excess sample was screeded fromthe cube molds 10 minutes after Vicat set and the cubes were carefullyremoved from the molds approximately 50 minutes later. About 24 hoursafter the cubes were made, they were placed in a 110° F. (43° C.) forcedair oven for eight days until constant weight was achieved.

Density of the samples was determined by weighing a number of driedcubes and applying the following formula:Density (lb/ft³)=(Weight of cubes*0.47598)÷number of cubes

Aggregated cubes were used to test for compressive strength using acompressive strength testing machine. Cubes were placed between twoplatens. Force was applied to the cube as the platens were pushedtogether. The machine recorded the pounds of force that were required tocrush the cube. Total force in pounds was converted to pounds per squareinch (psi) by dividing by the surface area of the sample, in this case 4in².

References to set time refer to Vicat set time per ASTM C-472, hereinincorporated by reference. The Vicat set time started from the time theplaster was added to the water for hand mixes and from the time theslurry came off the mixer for machine mixes. A sample was made up of 50grams of dry, aggregate-free material and sufficient water to make anormal consistency for the desired application. The sample was pouredonto an acrylic sheet to form a patty. A 300 gram Vicat needle was heldhalf way between the center and the outer edge of the patty,perpendicular to the patty surface. The needle was held to the pattysurface and released to fall freely of it's own weight. Set time wasdetermined when the needle failed to penetrate to the bottom of thepatty. If the degree of penetration was unclear, the needle was given alittle push to determine if it had touched the underlying surface.

EXAMPLE 1

A gypsum cement formulation suitable for use in a floor underlaymentproduct was made according to the present invention. beta-Calcinedgypsum was substituted for a substantial amount of the alpha-calcinedgypsum, and a high quality product was made with the addition of fromabout 0.025% to about 10% polycarboxylates.

TABLE I Floor Underlayment Composition Component 12–150 12–95 12–116beta-Calcined Gypsum 1780 2710 3775 alpha-Calcined Gypsum 1860 930 0Class C Cement 200 200 200 Defoamer 7 7 2 Boric Acid 5 5 5 CSA 0.25 0.250.25 Proteinacous Retarder 1 0.25 0.0938 Plasticizer Lomar 1641 1641Plasticizer Amount 12 17 27 Sand Type Mohawk Florida Rich MIx Water,cc/1000 g dry aggregate 185 195 185 Free components

The dry components were dry blended and 1185 gram samples were measured.Each sample was mixed with 2815 grams of sand, then all components wereadded to the water and blended. Results for slump tests, density andstrength are shown in Table II.

TABLE II Physical Properties of Floor Underlayments 12–150 12–95 12–116Slump, Inches 10 (25.4 cm) 9¾ (24.8 cm) 9¼ (23.5 cm) Dry Density, 121(1.94) 119 (1.90) 116 (1.85) lb/ft³ (g/cc) Strength, 2 Hr, 966 (67.9)1395 (98.1) 1095 (77.0) psi (Kg/cm²) Strength, 8 day 2454 (172.5) 3542(249.0) 2970 (208.8) Bleed water 0.829% 0.4666% None

EXAMPLE 2

The floor underlayment composition of Table III was studied to determineif sands with a high percentage of fines could be used in thecomposition. A Rich Mix Fine Sand and Mohawk Medium sand were studiedhaving the sieve analysis in Table III below.

TABLE III Sieve Analysis % Passing Mesh # Rich Mix Fine Mohawk MediumASTM C-33  #4 100 100 95–100  #8 100 92 80–100  #16 99.54 55 50–85   #3084.23 45 26–60   #50 11.56 15 3–30 #100 0.08 2 0–10

The Rich Mix sand is unusually high in the amount of material in themiddle range, passing through the #16 and #30 U.S. Standard sieves.Because fine sands require more water to fluidize the matrix, theincreased amount of water contributes to the settling of the sandcomponent and increased bleed water.

Samples (2370 grams) of the Base Floor Underlayment Composition of TableIV were measured. The control sample, designated 2–136 had nopolysaccharide added. The test sample, 2–138, had 0.3116 grams of DiutanEX-8259 added to the dry ingredients. To each sample, 1689 grams of aMohawk medium sand and 3941 grams of Rich Mix Fine Sand were added.Water was added to achieve a target slump of a 9½ patty when the slumptest was performed. Slump test results for both samples are detailed inTable V.

TABLE IV Base Floor Underlayment Composition Component QuantityBeta-calcined Gypsum 2710 Alpha-calcined Gypsum 930 Class C Cement 200Defoamer 7 Boric Acid 5 CSA 0.25 Retarder 1 Melflux 1641 23

TABLE V Slump Test Results for Floor Underlayment Sample 2-136 2-138Polysaccharide 0 0.004% Initial Slump, inches (cm) 9.75 (24.8) 9.5(24.1) Slump @ 5 minutes 11 (27.9) 10 (25.4) Slump @ 10 minutes 10.625(27.0) 9.375 (23.8) Slump @ 15 minutes 9.75 (24.8) 9.75 (24.8) Slump @20 minutes No Slump 9 (22.9) Slump @ 25 minutes No Slump 8 (20.3)

EXAMPLE 3

A premium near self-leveling gypsum cement composition was made with amixture of alpha and beta-gypsum, cement and polycarboxylates. Mixtureswith water demand considerably below theoretical could be prepared usingthe composition described above.

The Stabilizer referenced in this example is a physical mixture of 70%of alpha-calcined gypsum and 30% of polysaccharide by weight.

TABLE VI Compositions of Premium Floor Underlayments Component 2-1012-108 2-118 alpha-Calcined Gypsum 2110 2110 2110 beta-Calcined Gypsum1000 1000 1000 Class C Cement 560 560 560 Polycarboxylate 12 15 25Defoamer 0 0 2 CSA 0 0 0.3 Retarder 1.5 3.75 2.5 Stabilizer 0.5 0.5 0.5

Samples were prepared using 1333 grams of each of the above compositionsmixed with 2667 grams of a medium Mohawk sand. Water was added until aslump of 9½–9¾ inches (24.1 to 24.8 cm) was obtained.

TABLE VII Polycarboxylate Addition to Premium Floor UnderlaymentComposition Sample 2-101 2-108 2-118 Consistency, cc 160 150 135water/1000 g Slump, inches (cc) 9½ (24.1) 9 (22.9) 9¾ (24.8) DryDensity, 124.8 (2.0) 128.1 (2.05) 133.0 (2.13) lb/ft³ (g/cc) 2 Hr.Strength, psi 1417 (99.6) 1692 (119.0) 1825 (128.3) (Kg/cm²) 8 DayStrength, 4563 (320) 4883 (343) 5779 (406) psi (Kg/cm²)As the concentration of polycarboxylate increased, the amount of waterdecreased, density and strength of the product increased. At aconsistency of 135 cc/1000 grams of dry composition, the product hadless than the theoretical amount of water needed for complete hydration.Yet, the strength and density were not obtained at the expense of theflow properties.

EXAMPLE 4

An improved self-leveling floor composition comprises gypsum cement andpolycarboxylates and polysaccharides.

TABLE VIII Self-Leveling Floor Underlayment Composition Component AmountBeta-calcined Gypsum 1000 Class C Cement 950 Accelerator 10 50E200 40Melflux 1641 20 Defoamer 2 Oklahoma Sand 1400 Mohawk Fine Sand 600 CSA0.5

The above formula was used to determine how long the floor underlaymentcomposition would retain its self-healing properties after pouring.

TABLE IX Working Properties of Self-Leveling Compositions Time SinceMixing Comments 10 minutes Self healing 13 minutes Self healing 16minutes Self healing slowly 20 minutes Self healing slowly 23 minutesSelf healing slowly 28 minutes Edges drying, middle heals slowly 31minutes Edges drying, middle heals slowly 36 minutes Edges drying,middle heals slowly 43 minutes Middle heals very slowly 45 minutesMiddle soft, edges not healing

The data of this example shows that a self-leveling gypsum formula hasbeen achieved using all beta-calcined gypsum with good working time, asindicated above.

EXAMPLE 5

Finishing properties of the underlayment material was studied todetermine the ease with which the product could be finished. Aself-leveling flooring composition was prepared with the amounts of allcomponents shown in Table VIII, but with the amounts of Polycarboxylate,50E200 Polymer and polysaccharide stabilizer modified as follows:

TABLE X Floor Finishing Samples Sample 145A 145B 145C 167 Melflux 164118 17 17 17 Retarder 0.75  0 0 0.5 50E200 0  0 0 0 Water, per 100 g 3033 33 33 Slump 12   11½ 8 10 Working Time — 30 20 30 Finishing PinrolledSets Too Pinroll Pinrolled Well slow Left Ridges Well

EXAMPLE 6

Fluidity of a flooring composition was tested by comparing the additionof polysaccharide compared to a sulfonated naphthalene. The compositionsof the base flooring composition is supplied in Table XI below:

TABLE XI Base Floor Underlayment Composition Beta-calcined Gypsum 1232grams Class C Cement 100 grams Defoamer 5.33 grams Set Accelerator0.08333 grams Sand 2667 grams

This example examines the amount of polycarboxylate needed to yield aslump of 9½ inches compared to the amount of a sulfonated naphthaleneplasticizer needed for the same slump. The plasticizer was added to thebase flooring compound in amounts shown in Table XII.

TABLE XII Slump Test Results for Sulfonated Naphthalene andPolycarboxylate Superplasticizers Sample 11-136A 11-136B 11-136C BaseFlooring Cmpd, g 1333 1333 1333 Plasticizer Used MVA 1641 Lomar D LomarD Plasticizer Amount, g 2.24 2.24 8.325 Slump, inch (cc) 9½ (24.1) None9¼ (23.5) Set Time 62 min. 80.5 min. Strength, 2 hr, psi 8292 (583) 5856(412) (Kg/cm²) Strength, 8 day 5908 (415) 4125 (290) Dry Density, 129.92(2.08) 92.80 (1.48) lb/ft³ (g/cc) Bleed Water None 0.0095%

The amount of sulfonated naphthalene plasticizer, Lomar D® needed wasalmost four times the amount of polycarboxylate, MVA 1641, to obtain thesame fluidity for a flooring composition. At the same fluidity, theflooring of sample 11-136A was stronger, denser, set faster and had lessbleed water, resulting in a superior product. When the two plasticizerswere used at the same concentration, as in Samples 11-136A and B, Sample11-136B was too thick to spread at all.

The embodiments and examples shown herein are intended to exemplify theinvention and are not intended to limit it in any way. Optionalingredients of the composition can be combined in any useful manner withany embodiment of this invention. Additional embodiments and uses forthis invention will be apparent to an artisan in this particular field.

1. A mixture to be employed in conjunction with water for preparing aslurry that hydrates to form a high strength flooring compound,comprising: about 50% to about 98% by weight calcium sulfatehemihydrate, at least 25% of said calcium sulfate hemihydrate being thebeta-calcined form; about 0.2% to about 10% by weight of apolycarboxylate dispersant comprising a copolymer of anoxyalkylene-alkyl ether and an unsaturated dicarboxylic acid; and0.05–50% by weight enhancing component.
 2. The mixture of claim 1wherein said calcium sulfate hemihydrate comprises at least 90% byweight of the beta-calcined form.
 3. The mixture of claim 2 wherein saidcalcium sulfate hemihydrate consists essentially of the beta-calcinedform.
 4. The mixture of claim 2 wherein the concentration of saidhemihydrate is from about 80% to about 95% by weight.
 5. The mixture ofclaim 1 wherein said enhancing component comprises lime.
 6. The mixtureof claim 5 wherein the concentration of said lime in said mixture isfrom about 0.05% to about 10% by weight.
 7. The mixture of claim 1wherein said mixture comprises from about 0.2% to about 1% by weightpolycarboxylate on a dry, aggregate-free basis.
 8. The mixture of claim1 further comprising polysaccharide.
 9. A subfloor comprising a hydratedproduct of a pumpable slurry comprising: about 50% to about 98% calciumsulfate hemihydrate, said hemihydrate comprising at least 25% of thebeta-calcined form; about 0.2% to about 10% of a polycarboxylatedispersant comprising a copolymer of an oxyalkylene-alkyl ether and anunsaturated dicarboxylic acid; about 0.05% to about 50% enhancingcomponent; and from about 12 cc to about 40 cc water per 100 grams of acombined mixture of the hemihydrate, the polycarboxylate and theenhancing component on a dry solids basis, said hydrated mixture havinga compressive strength in excess of 2500 psi (175 Kg/cm2).
 10. Thesubfloor of claim 9 wherein said hemihydrate consists essentially ofbeta-calcined hemihydrate.
 11. The subfloor of claim 9 wherein theconcentration of said polycarboxylate dispersant is from about 0.2% toabout 1% by weight on a dry, aggregate-free basis.
 12. The subfloor ofclaim 9 wherein said enhancing component comprises lime.
 13. Thesubfloor of claim 11 wherein said water is present in an amount lessthan 35 cc water per 100 grams mixture on a dry, aggregate-free basis.14. The subfloor of claim 13 wherein said water is present in an amountless than 25 cc per 100 grams of said mixture on a dry, aggregate-freebasis.
 15. The subfloor of claim 8 wherein said slurry further comprisespolysaccharide.
 16. A subfloor comprising a hydrated product of apumpable slurry comprising: about 50% to about 98% calcium sulfatehemihydrate, at least 25% of said calcium sulfate hemihydrate being thebeta-calcined form; about 0.2% to about 10% of a polycarboxylatedispersant comprising a copolymer of an oxyalkylene-alkyl ether and anunsaturated dicarboxylic acid; about 0.05% to about 50% enhancingcomponent; and from about 15 cc to about 25 cc water per 100 grams of acombined mixture of the hemihydrate, the polycarboxylate and theenhancing component on a dry solids basis, said hydrated mixture havinga compressive strength in excess of 2500 psi (175 Kg/cm2).
 17. A methodof preparing a subfloor comprising: obtaining ingredients comprisingfrom about 50% to about 98% calcium sulfate hemihydrate comprising atleast 25% of the beta-calcined form, from about 0.2% to about 10% of apolycarboxylate dispersant comprising a copolymer of anoxyalkylene-alkyl ether and an unsaturated dicarboxylic acid; and fromabout 0.05% to about 50% of an enhancing component, all on a dry solidsbasis; separating the ingredients into wet ingredients and dryingredients; dry blending the dry ingredients; measuring from about 12cc to about 40 cc of water per 100 grams of the ingredients on a drysolids basis; forming a mixture of the wet ingredients and the water;forming a slurry from the dry ingredients and the mixture; pouring theslurry in an area prepared for the subfloor; and, allowing the slurry toset, forming the subfloor having a compressive strength in excess of2500 psi.
 18. The method of claim 17 wherein the calcined gypsumcomprises beta-calcined gypsum.
 19. The method of claim 17 wherein saidcalcium sulfate hemihydrate comprises at least 80% by weight of the drymixture on an aggregate-free basis.
 20. The method of claim 17 furthercomprising the step of mixing an aggregate into the dry ingredientsprior to forming the slurry.
 21. The method of claim 17 furthercomprising packaging the dry mixture after said dry blending step.
 22. Asubfloor comprising the hydrated product of the process of claim 16.